Scanning and focusing yoke



Jan. 28, 1947. I BUCKBEE I 2,414,925

SCANNING AND FOCUSING YOKE Filed Jan. 26, 1944 INVENTOR JOHN BUCKBEE Patented Jan. 28, 1947 SCANNING AND FOCUSING YOKE John A. Buckbee, Fort Wayne, Ind., assignor to Farnsworth Television and Radio Corporation, a corporation of Delaware Application January 26, 1944, Serial No. 519,719

4 Claims. 1

This invention relates generally to electromagnetic toroidal coils and more particularly to a toroidal scanning yok for cathode ray tubes.

Conventional scanning yokes for cathode ray tubes generally include coils laid about the exterior of. a cathode ray tube in such fashion that the electromagnetic field threads through the interior space enclosed by the coil into the path of the electron beam in the tube and around the exterior surface of the coil. Such coils are inefiicient in that a large percentage of the field is exterior to the tube and does not operate to deflect the electron beam within the tube. Consequently, a large portion of the energy converted by the coil is dissipated. Furthermore, the exterior portion of the field tends to create electrical disturbances in equipment associated with cathode ray tubes in their conventional applications. Conventional scanning yokes also do not provide in a cathode ray tube an electromagnetic field having a uniform intensity. Consequently, the deflection of the electron beam is not proportional to the deflecting potentials.

Accordingly, the principal object of this invention is to provide a novel scanning yoke for cathode ray tubes characterized by its ability to generate a magnetic field of uniform intensity throughout the field intersected by the cathode ray.

Another object of this invention is to provide an electromagnetic scanning yoke for cathode ray tubes characterized b its ability to concentrate an electromagnetic field in the area, traversed by the electron beam whereb to minimize the generation of an electromagnetic field exterior to the tube envelope.

Still another object of this invention is to pro vide a novel scanning yoke for cathode ray tubes wherein substantially all energy applied to the coil is utilized for deflection purposes.

In accordance with this invention, there is provided for use with a cathode ray tube an annular ferromagnetic core consisting of a continuously Wound thin strip of transformer iron whereby to provide a plurality of laminations.

For deflecting the electron beam in one direction, there is provided a pair of separate coils each of which is Wound around the core to form a toroid and provide adjacent south poles and adjacent north poles which are spaced 180 apart.

For poling the yoke in this manner, the coils may be wound identically and electrically connected in parallel or they may be wound oppositely in direction and electrically connected in series to a source of potential.

For providing deflection of th cathode ray in a direction displaced with respect to that of the first pair of coils, a second pair of coils are wound about the first pair except that they are displaced 90 with respect to those coils. This second pair of coils ma be similarly arranged to provide adjacent south poles and adjacent north poles as described hereinbefore in connection with the first pair.

The scanning yoke, in accordance with this invention, may also include a focusing coil circumferentiall wound around the exterior of the deflecting coil assembly whereby to provide a focusing magnetic field for controlling the focus of the electron beam in the cathode ray tube. It is not necessary that the focusing coil be wound about the exterior of the deflecting coils, as it is found that the focusing coil will be equally effective when wound inside the deflecting coil assembly.

For a better understanding of th invention, together with other and further objects thereof, reference is made to the following description, taken in connection with the accompanying drawing, and its scope will b pointed out in the appended claims.

In the accompanying drawing:

Fig. 1 is a plan view in cross-section of a cathode ray tube and scanning yoke as provided by this invention.

Fig. 2 is a side elevation of Fig. 1 with parts broken away to illustrate the structural relationship of the various coils to one another and to the magnetic core.

Fig. 3 is a cross-section taken on line 3-3 of Fig. 1.

Fig. 4 is a schematic diagram illustrating the electrical relationship of the various coils to one another and their electrical connections.

Fig. 5 is a diagram illustrating the field distribution within the space enclosed by the scanning yoke illustrated in Figs. 1 to 3.

Referring to the drawing, there is provided in accordance with this invention a cathode ray tube I of conventional construction and. including an electron gun assembly 2 for generating an electron beam for scanning a fluorescent screen 4. The invention is illustrated in connection with a cathode ray tube adapted to reproduce a signal on a fluorescent screen, but it is to be understood that the invention is equally applicable to any form of cathode ray tube including the iconoscope and the dissector which are television transmitting tubes.

The scanning yoke consists of a laminated ferromagnetic core 5 which may be formed by winding a continuous ribbon of transformer iron to form a laminated ring of, for example, A in thickness. About the core 5 there may be wound vertical deflection coils l and 8. The coils may be wound identically and placed opposite to one another on the core and connected in parallel, or they may be wound oppositely to one another and connected in series with one another to a source of potential as indicated in Fig. 4. In either case there are magnetic south poles adjacent to one another, for example, at the top portion of the ring and magnetic 'north poles at i the lower portion of the ring as shown in Fig. 4. It will be obvious to those skilled in the art that there are other methods of arranging the coils and their connections to obtain the same results.

By means of this arrangement, the electromagnetic field is substantially uniformly distributed across the area traversed by the electron beam. Furthermore, the field generated by the coils is within the laminated core and within the envelope of the tube i whereby a major portion of the energy applied to the coils is effective to deflect the electron beam and Very little of the energy applied to the coils causes any external interference effects with respect to other apparatus associated with the cathode ray tube.

Horizontal deflection coils 9 and ID are wound around vertical deflection coils l and 8 and displaced 90 with respect to coils I and 8 whereby to generate a field at right angles to that generated by coils l and 8. The field generated by coils 9 and I!) is effective in the same manner as already described hereinbef ore in connection with coils 7 and 8 except that it is displaced 90.

For focusing the electron beam there is provided a focusing coil I 2 wound about the outer circumference of coils 9 and If]. It is found that such construction does not deleteriously affect the field generated by the deflection coils and it in turn does not deleteriously affect the focusin field generated by coil H2.

The scanning yoke constructed as described hereinbefore and consisting of uniformly Wound coils generates an electromagnetic field which is substantially uniform throughout the area traversed by the electron beam in tube 5. However, it can be shown that coils I, 8, 9 and I will produce an absolutely uniform'field when wound to have sinusoidal distribution of turns. Referring to Fig. 4 of the drawing, let it be the number of coil turns per unit width of current sheet around the coil. In order to fulfill the condition where the magnetic field is uniform, 11. must be proportional to sin 0. Thus the winding must be spaced more closely where the y axis cuts the ring where the field H is in the a: direction. Also it will be larger at the point where r=r1 than at the point where r=r2 because where r=r1 there is less space for the same current to flow than at T2. 'Iherefore, to calculate the number of turns in the coil at any given point on the coil, the following equation applies at 1*:11:

n=N sin 0 or, at r=fz the following equation applies:

The factor To is some ratio between 11 and r2 where there are No sin 0 turns per centimeter. For simplicity, it may be assumed that o We be limited to the exact form illustrated in the drawing as it has been found to be equally effective when wound within the interior circumference of coils 9 and illand directly adjacent the tube envelope. Further, it is not necessary that the core be laminated as powdered iron cores are also possible.

With respect to the scanning yoke, it is to be noted that this invention is not limited to the use of two pairs of scanning coils. The invention is equally applicable to a scanning yoke for producing cathode ray deflection in a single direction. Thus a cathode ray tube may be provided to include a scanning yoke having a single pair of coils for producing a unidirectional field in whatever direction ray deflection may be desired.

While there has been described what is at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and mod ifications as fall within the true spirit and scope of the invention.

W hat is claimed is:

1. An electromagnetic deflecting system for a cathode ray tube comprising an annular laminated ferromagnetic core disposed about the electron path of said tube, a first deflecting coil comprising two portions each of which is wound about said core and energized to provide a unidirectional electromagnetic field within the space enclosed by said core, a second deflecting coil displaced with respect to said first coil and comprising two portions, each of which is wound about said first coil and energized to provide a unidirectional electromagnetic field within the space enclosed by said core and 90 displaced with respect to said first field and a focusing coil wound with respect to said core to provide an electron focusing field.

2. An electromagnetic deflecting system for a cathode ray tube comprising an annular laminated ferromagnetic core disposed about the electron path of said tube, a first deflecting coil comprising two portions electrically connected in series and wound in opposite directions about said core to provide a unidirectional electromagnetic field within the space enclosed by said core and a second deflecting coil displaced 90 with respect to said first coil and comprising two portions electrically connected in series and wound in opposite directions about said first coil to provide a unidirectional electromagnetic field Within the space enclosed by said core and 90 displaced with respect to said first field.

3. An electromagnetic deflecting system for a cathode ray tube comprising an annular core disposed about the electron path of said tube, a first deflecting coil comprising two portions each of which is wound about said core and displaced with-respect to one another, asecond deflecting coil displaced 90 with respect to said first coil and comprising two portions each of said core to provide a unidirectional electromagnetic field within the space enclosed by said core, a second deflecting coil displaced 90 with respect to said first coil and comprising two portions electrically connected in series and wound in opposite directions about said first coil to provide a unidirectional electromagnetic field within the space enclosed by said core and 90 displaced with respect to said first field and a focusing coil wound about the periphery of said second deflecting coil.

JOHN A. BUCKBEE. 

